Sensors, in general, are devices used to detect physical stimuli such as heat, particulates, chemicals, gasses, etc. and output a signal that may be used to quantify the stimuli. Over time, a sensor's response to stimuli may change, which may in turn affect the accuracy of any quantification based on the output signal.
In order to account for this change in sensor response, sensor manufacturers typically provide specifications having a relatively wide range of operating parameters so that, even after the change, the sensor will most likely still be in the range. However, knowing that a sensor is operating within this operating parameter range may not be sufficient for a user of the sensor who may have calibrated the sensor based on a pre-change response curve.